Selective separation and recovery of Sr from environmental ions by lanthanide oxalate frameworks

Nankawa, Takuya ; Sekine, Yurina   ; Yamada, Teppei*

Among the radioisotopes to be removed, Sr, which has a radioactive half-life of 28.8 years, poses a major threat to human health and the environment because of its uptake and retention in biological systems. However, removal of Sr from wastewater is still challenging due to the difficulty of separating Sr from Ca. Ca has a similar properties and ionic radius to Sr. Indeed, the difference in their ionic radii is only 0.2 . Furthermore, the concentration of Ca in actual nuclear wastewater is usually much higher than that of Sr, which limits the efficient removal of Sr. Here, we developed a series of isostructural lanthanide oxalate frameworks (LOFs) comprising oxalate and eight kinds of lanthanide (Ln) ions, i.e., from Sm to Tm, for application to selective removal of Sr from wastewater using its tuned porous structure. When Tb was the host Ln of the LOF, the LOF showed extremely high Sr selectivity and was able to distinguish the subtle difference in ionic radius between Sr and Ca. This novel pore size tuning strategy will be useful in developing custom porous materials that are easy to prepare and applicable across various fields.